Patent GB-444256-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1934-09-17
Abstract: 444,256. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool, and PEARCE, O. A., 107, Quarry Street, Woolton, and RICHARDS, I. T., Ealing, Renville Road, both in Liverpool. Sept. 17, 1934, No. 26705. [Class 40 (iv)] Two different classes of operators have access to the same group of trunks and in case of an all trunks busy condition, a signal is adapted to be given to the operators when a trunk becomes idle, but if both classes are waiting for an idle trunk, the signal is given to one class only. The invention is described with reference to a system employing both long distance and demand operators, the long distance operators having the preference. Long distance operators LD, Fig. 1, and demand operators DM have access to separate groups of first selectors TS1 which, over one wiper set, have access to second selectors TS2 having outlets over relay sets BW to groups of junctions to a number of exchanges. In response, however, to a particular digit, selectors TS1 drop back and hunt over the levels of the second wiper set forming one large group leading to an exchange P, overflow calls in this group being stored at CS1 which is seized over different paths by different classes of operators so that it signals only the long distance operators when a trunk becomes idle. Overflow calls in the groups accessible to TS2 are stored at CS2 a signal from TS1 being passed by TS2 to CS2 when a long distance operator has made the call. Rotary hunting at a 2nd selector is initiated on receipt of digit 1, but the switch may be stepped to. a particular outlet by any other digits. The switches, on release, step forward out of the banks, drop and return to normal. Long distance operator extends call to exchange other than P, Figs. 2 to 6. On plugging the jack, Fig. 2, sleeve relay B lights the engaged lamps VES at the operators' positions preferably from a 6-volt A.C. source, and energizes C which starts SF searching for a sender. A busy sender grounds P to operate stepping relay MC over K which remains inert. SFM and MC interact until idle battery shunts MC and operates K over both windings, this relay holding over its low resistance winding and grounding wiper D to prevent a register-controller from being associated with the sender. While SF hunts, relay LP is pulsed by an interrupter and shortcircuits DR to flash the cord lamp. When K switches through, the in-and-out circuits of the sender are completed, A and BB pull up and the flashing ceases. When the number has been keyed, the first digit from the sender is repeated by A over C (lower) to VM, the original circuit for C (upper) being opened at the first step. The relapse of C at the end of the train makes a self interrupting circuit for RM which rotates the selector until idle battery over P1 operates T over both windings in series. Relay H pulls up in series with RM and as the current over the lower winding of T has been reversed, T will only hold if no other selector is testing the same outlet. Specification 435,411 is referred to for this feature. Relay H opens the circuit of T and switches through. Relays A, BB pull up at the second group selector, Figs. 5 and 6, and B operated over the third wire energizes C. The second digit is repeated to VM and when C relapses change - over relay E pulls up and re-operates C which holds E. If hunting is to take place, a digit 1 is received and repeated to RM, the circuit of C (lower) being opened at NR2 so that C falls back when the impulse terminates and E follows slowly, but in the meantime PS (lower) energizes over wiper P (first contact), locks over its upper winding for the remainder of the connection, and prepares a self-interrupting circuit for RM which is completed by the relapse of E. Hunting may also be initiated by the operation of PS over post springs NP. Test and switching relays operate as described for the 1st group selector, and the completion of the connection is effected by an incoming operator. When the called party replies, the outgoing relay set returns battery over the S wire to operate F, Fig. 4, which removes a short circuit on DR, Fig. 2, to extinguish the supervisory lamp, DR remaining inert since a differential circuit is also closed by F. All outlets busy. If the 1st selector finds all outlets busy, battery (not shown), on wiper P1 causes the switch through and cam springs connect up busy tone. The busy condition at the 2nd selector causes the call to be stored in, and a discriminating signal to be sent to, storage equipment, Figs. 7 and 8, as will be described later. Abnormal conditions in sender. These cause ground to be connected to lead FR, Fig. 3, to operate M which shunts down K to disconnect the sender and releases H which releases the connection subsequent to the first selector, N.U. tone being sent to the operator. Release. When the operator withdraws, B, H and F fall back, the rotary magnet RM steps the switch out of the bank whereupon the switch drops and returns to normal. L.D. operator calls exchange P. The discriminating first digit 1 (other digits may also be used) raises the wipers of the first group selector to level 1 where on the relapse of C post springs NP1 operate DA which makes a self-interrupting circuit for RM to release the selector. On reaching normal, C (upper) is re-operated and energizes DB which locks, connects up the lower set of wipers, and makes a self-interrupting circuit for vertical magnet VM. When a level containing an idle junction is found, battery on vertical bank AW operates T to stop the hunting and release C which releases T, connects it to the test wiper P2, and makes a self-interrupting circuit for RM, an idle outlet being seized as previously described. All outlets to exchange P busy ; storage of call. The selector steps to 11th position on the last level whereupon T and H operate in response to battery over BB, Fig. 12, at the call storage equipment, and cam springs S connect interrupted N.U. tone to the jack. The selector remains in this condition until it receives a signal that a junction has become idle. At the storage equipment, Figs. 12 to 14, relay GP operates on an all trunks busy condition due to absence of ground on common lead 14, and position lamps TCL, Fig. 14, light up. Relay BB, Fig. 12, disconnects two of the 11th step leads from demand operators' first selectors to prevent these selectors getting a " trunk idle " signal while long distance operators are waiting. Relay LC, Fig. 13, is operated by battery over springs S2 at the group selector, and advances IN one step by operating R and V, these relays and LC being released by magnet INM, and LC being prevented from re-operating by battery over IN2 and a differential winding. The contacts of IN2 and 3 are connected to batterv over resistances of different values to provide a balance over the differential winding of LC for the number of selectors connected to its operating winding. Storage lamp SL1, Fig. 12, is lit by A which operates over IN4, and lamps SL6-10 are disconnected by Y operated over IN5 since these lamps are also controlled by relays A ... E. If a second call is received on the storage set, relay LC (right hand) receives additional current from battery at another selector to unbalance it, IN takes a further step to rebalance LC over IN2 and to energize B which lights the second lamp SL2. A remains held in series with B. Further calls are stored in a similar manner, IN3 being used to help in balancing LC and Y being released at the sixth call to prepare the circuits of SL6 ... SL10, lamps SL2 -SL5 being maintained by the operation of X since relays B ... E are released and A held on receipt of this call. Any contact of IN1 may be connected to OFA and this relay operates over key CCK assumed thrown to the left by the supervising operator, so that after any desired number of calls have been stored, OFA operates the delay lamps DL to inform operators that further calls must proceed on a delay basis. Delay working can be commenced at any time when the supervisor throws CCK to the right. When a junction becomes idle, GP relapses and connects an interrupter to LF which intermittently connects battery over IRR (upper) to relay F, Fig. 4, to flash the cord lamp. The lower differential winding of IRR is also intermittently made so that IRR remains inert. When the operator proceeds with the call by increasing the current over the sleeve circuit DR connects battery to wiper S2 thereby unbalancing IRR which releases LF and grounds the + wire to operate RR, Fig. 4, which releases H so that the selector releases RR falls back and hunting re-commences. The balance on LC in the storage equipment is upset by the release of the selector so that IN steps on until the balance is again restored, the number of lamps SL remaining lit being reduced by one. Calls by demand operators. The 1st selectors, Figs. 9-11 (not shown) operate in the substantially the same manner as long-distance operators' 1st selectors to extend calls either to 2nd selectors or to outgoing junctions to exchange P, the same 2nd selectors and call storing equipments being accessible to both classes of operators. As regards the storage equipment Figs. 12-14 for P calls, storage is effected by the operation of BA instead of by BB, but if a long distance operator is awaiting a free junction (BB operated) the S-wire is open and the junctionfree signal is prevented from passing to the demand operators. The demand operators' 1st selectors do not send the booster discriminating signal described in the next paragraph. Storage apparatus, Figs. 7 and 8, for calls to exchanges other than P. This is substantially the same as that shown in Figs. 12 to 14 for exchange P but discrimination between the two classes of operators is effected differently. When a long distance switch train is used, LP, Fig. 2, operated during the hunting of the 1st selector, is released when H switches